The problem is that usually such a list and the related HTML is created by Limesurvey on page load. That being said, I think the best approach is to have just one fixed answer like "I don't know" and then use some javaScript which on page load queries the database to get a list of answers. This can be done via Ajax.
Please also note that you need to assign a unique key to each answer. That is the answer code which will then be stored by Limesurvey.

A follow up problem will show up later when viewing or exporting the responses, because Limesurvey will search for the answer code at the Limesurvey database to query for the full answer string and this data will NOT exist if you load the list from an external DB.
So you should also consider updating the Limesurvey database with that data once a certain answer was selected by the user.